Pressure in Cooling Expansion Bottle

[Giles]

Hi

Am in the process of buying my first stag.

I have been looking at a few stags to buy. One that I looked at today is very good - spot on!, the only concern iswhen warmed up from cold if you take the cap off the expansion bottle there is no pressure - normally you would get a 'woosh' of air as the pressure escapes on other cars but that would be on a header tank.

Is this normal on a stag as it is a expansion bottle and not a header tank - different from other cars I have had. They had expansion tanks that were not pressurised but the stag one looks as if it should be ?

I cannot find any leaks, it does not overheat, there is no sign of water in the valley or out of the exhaustand the engine runs very sweetly. The dealer is happy to do a sniff test.


I have justthought -the metal seat for the cap turns on the plastic bottle - do they tend to leak around that joint?

thanks

[Bob Heritage]

imported post

Hi Giles

There should be pressure in the expansion bottle when the engine has warmed up, a Mk 1 car is 13lb and a Mk2 car is 20lb, it could be something simple like a faulty pressure cap, get the dealer to replace it and have another look.

Bob

[Mark S]

imported post

Ifits a Mk2 with the pressure cap on the bottle,then it should hold pressure.The metal collarto plasticneck joint can leak, and almost certainly will if the seal has been broken and the collar can turn. In the pastI have used a smear of blue Hylomar around the internal joint between metal and plastic which sealed it for a while.

The rubberon a20lb cap that I bought a couple of years ago was so thin that it leakedthe first time it was disturbed!

A better solution is to modifyusing a modern two pipe bottle mounted higher than the rad.

A pressure testwith compressed airis the best way to findif or where the leaks are IMHO.

Mark.